Color-blind persons (persons having various inabilities to distinguish colors) are often unable to reliably distinguish colors of various objects (colored objects, lights, indicia, etc.) wherein the color thereof is important or even critical to accurate interpretation of the object. Common examples of such objects include lighted and non-lighted signals, indicators and signs used for controlling vehicle, pedestrian and air traffic, for operating household, industrial and transportation equipment, and any source of light and/or other visual information wherein color is important or even critical to accurate interpretation of the information.
Vehicle drivers who are color-blind generally rely on indications other than color such as the relative positions of traffic signal lights (not always standardized and therefore not to be ubiquitously trusted) or the movement of other traffic. Aircraft pilots who are color-blind are not permitted to fly during hours of darkness because the ability to distinguish colors is considered critical to the accurate interpretation of lighted, colored signals and markers at airports. Operators of equipment having indicators wherein color thereof has significance must rely on labels or other aids to interpret the significance of lighted signals.
U.S. Pat. No. 4,300,819 to D. E. Taylor describes eyeglasses for distinguishing colors using one colored and one clear lens. Such a device is limited in effectiveness in that only one color can be distinguished. Moreover, such a method is not generally effective for persons with significant visual acuity in only one eye. See also U.S. Pat. No. 3,586,423.
U.S. Pat. No. 4,998,817 to H. I. Zeltzer describes a corneal contact lens for the distinguishing of colors, which is clear except for a thin red exterior layer covering the area admitting light to the pupil. Such a device is also limited in effectiveness in that only one color can be distinguished, and it is not generally effective for persons with significant visual acuity in only one eye.